Vocabulary and Synonyms

Gradual means taking place, changing, moving, etc. by small degrees or little by little and continuously.

Someone who is generous gives freely. Hence, freely is correct.

Insinuate means to hint or suggest indirectly; imply.  

Incite and rouse are synonyms. Incite means to encourage or stir up violent or unlawful behaviour. Rouse means to stir or incite to strong indignation or anger. 

Jumble is a mixed assortment of items; and so is miscellany.

To keep something means to hold or possess something.

Lofty and giant are synonyms. Lofty means of imposing height.

Knack and expertise are synonyms. Knack means an acquired or natural skill at doing something.

Luxuriant means something abundant or thick.

A mature person is someone who is fully developed or experienced.

Magnificent describes something grand, impressive, or beautiful. Splendid is the closest synonym among the options, sharing similar connotations of grandeur, excellence, and visual impressiveness.

Nurture means to bring up; train; educate.

Notorious means widely known for some negative quality or deed. Infamous is the precise synonym, also conveying fame for unfavorable reasons or disgraceful notoriety.

An enigma is something that is mysterious, puzzling, or difficult to understand. Puzzle (A) is the correct synonym because it directly represents something that requires solving or understanding. Reply, Sharp, and Praise are unrelated to the concept of mystery or puzzlement that enigma conveys.

An exponent is someone who supports, advocates for, or represents a particular idea, cause, or belief. Representative (A) captures this meaning - someone who speaks for or represents something. Messenger, Conductor, and Translator refer to different roles and don't capture the sense of advocacy or representation that exponent implies.